Study On The Key Technique And Property Of The Soil Tunnel Under Shallow-buried Excavating

Under the conditions of shallow-buried soil tunnel, the mechanics behavior of soil tunnel is a complicated problem which involved in wide range and greater difficulty. Therefore, the study on the key technique and property of shallow-buried soil tunnel with large-section has the important academic and practical value. Based on the construction of Tian-heng mountain soil tunnel, the paper mainly researched the behavior of mechanics and deformation, the proper and applicable methods of construction and bracing anchor by making use of theoretical analyses, numerical algorithm, prototype modeling, centrifuge modeling and so on. The main achievements are followed:1. The method of "marginal three bench excavation" which is proposed based on "excavation method by three stairs and seven steps" not only successfully deal with the soft stratum of Tian-heng mountain in construction, but also attain the aim of fast, safe and economical construction.2. Focus on the characteristic of the systematic anchor having no effect on the uniform displacement of shallow-buried soil tunnel, thus in order to reduce the cost and time limit of the tunnel engineering, the study recommend the anchor pipe of locking arch foot which could be used the pressed installment stead of the systematic anchor.3. By making use of three-dimensional finite element numerical analysis for Tian-heng mountain tunnel with CRD construction method, results show that the closer the excavating position is, the small rock the pressure is, and the rock pressure maintains the initial stress far from the position of excavation. Furthermore, the direction of principal stress which vary with the excavating process result in the different trend of failure corresponding to the different excavating method. Because the corner force of bracing structure is bigger, the corner of bracing structure needs to be reinforced. In addition, it is the cautious and important step in dismantling process that the force of the moldboard and the inverted arch will increase when they are dismantled.4. Based on the monitor measuring data of Tian-heng mountain soil tunnel construction, the stress distribution of surrounding rock is non-uniform and the maximum is located in the corner of bracing structure, while the stress distribution of excrete is nearly uniform and the maximum is located in vault. Furthermore, the analyses of data also show that the steel truss and longitudinal connecting steel reinforcement have effect on the integrity and stability of the preliminary reinforcement of tunnel. Based on the measuring data of the secondary lining, on the one hand the measured stresses of the secondary lining are smaller than the specified value of standard; on the other hand, both compressive and tensile stresses of steel reinforcement are smaller than the yield strength. Thus, the secondary lining works well done with enough safe reserve.5. By making use of two-dimensional finite element numerical analysis for Tian-heng mountain tunnel with CRD construction method and "marginal three bench excavation", results show that CRD construction method is beter for tunnel deformation and soil settlement because of its horizontaland and vertical temporary support.But, its Multi-step sequence excavation, support structure into the ring for a long time and horizontaland vertical temporary support need to be removed at a later are lead to the larger final settlement, so the design and Construction should be attention.6. Based on the study of the surrounding pressure of Tian-heng mountain soil tunnel, the soil column method was recommended and adopted for the design of shallow-buried soil tunnel. Furthermore, the differentiated standard of the shallow-buried and deep-buried soil tunnel should be determined by theoretical analysis and numerical calculation.7. The soil parameters have much influence on the analysis of mechanical properties of lining structure. According to the incidence of these soil parameters, the sequence which has different role in the application is such as E,μ,ψand C. Thus, the parameters of E andμnot only should be paid close attention to the influence in theoretical analyses and numerical calculation, but also concerned in experimental determination.